The charges come just over a week after the state-run NTV channel aired what it said was secretly filmed footage of a meeting between Udaltsov and a leading Georgia politician, the Russian news agency RIA Novosti reported.
In the video filmed in Minsk, the two men are seen discussing plans to seize power in cities across Russia, including the Baltic exclave of Kaliningrad.
Uldaltsov charged the video was a fake and said it represented the start of a new "wave of repression" targeting leaders of the protest movement against Russian President Vladimir Putin.
Udaltsov wrote on Twitter that he was taken to the headquarters of the Investigative Committee Wednesday after police searched his Moscow apartment.
His lawyer said he could be kept in custody.